The present invention relates to processes for the production of glycol ethers and more particularly to the catalyzed production of glycol ethers.
It is known to react organic compounds having at least one aliphatic hydroxyl group with oxirane compounds to obtain glycol ethers. Aspects of these known processes are shown in U.S. Pat. Nos. 2,684,387; 3,972,948 and 3,935,279. A range of reactants, catalysts and reactant conditions are shown to produce products having many utilities, for example, as components of brake fluids, cleaning fluids, solvents for dyes, paints, and lacquers and as chemical intermediates. In particular the mono adduct (n=1) of glycol ethers having the formula ##STR1## wherein R is an organic group, R' is hydrogen or an organic group and n is a positive integer, is a preferentially valued product relative to the higher adducts (n.gtoreq.2) under certain market conditions. Enhancement of the mono adduct (n=1) component in the product mixture resulting from the reaction of oxirane compounds with hydroxyl group containing compounds can be economically advantageous. Correspondingly, limiting the production of the higher adducts (n.gtoreq.2), commonly called highers, as well as limiting formation of glycols, polymers and by-products is often deemed desirable. Achieving this selectivity with reduced recycling, reprocessing and/or separation costs is particularly desirable. Therefore, process parameters including catalysts that may be successfully incorporated into a process to economically provide a degree of selectivity and control over the resultant product mix are much sought after in the industry.
Many catalysts have been used in the reaction of an oxirane compound with compounds having hydroxyl groups. Each has its own relative advantages and disadvantages. Acid catalyzed and base catalyzed reactions both yield hydroxyethers; see e.g. Morrison and Boyd, Organic Chemistry, 3rd Ed., (1973), p. 564. Acid catalysts allow production at lower temperatures than bases, but form undesirable byproducts; see e.g. U.S. Pat. No. 3,954,884 which describes the use of sulfuric acid, toluene sulfonic acid, sulfonated polystyrene and sulfonated styrene-divinylbenzene copolymers among others as catalysts. Alkali metal and alkaline earth metal hydroxide bases have been commonly used as catalysts in the reaction, in addition to those patents mentioned above, see, for example, European Patent Application No. 6105. These catalysts require removal or neutralization before purification of the product. The typical base catalysts NaOH and KOH introduce water into the reaction mixture from alkoxide formation. This results in consequential glycol impurities. Also both strong acid and strong base catalysts tend to be corrosive. The catalyst removal techniques employed, e.g. distillation, acid neutralization with distillation and/or filtration all result in additional energy requirements, yield losses or large waste streams. Thus, prior art catalysts have had problems achieving the goals of noncorrosivity, low by-product formations, ease of separation and catalytic effectiveness.
A heterogeneous catalyst obviates some of the above-mentioned problems associated with separating the catalyst from the reaction mixture. Such catalysts which are insoluble in the reaction mixture have been sought and polymeric materials have been used as such with varying degrees of success; see, e.g. U.S. Pat. No. 4,011,268 which describes the use of polymeric materials having tetraalkyl phosphonium alkoxide, aryloxide or hydroxide containing pendant groups. These catalysts have disadvantages including early deterioration at reaction temperatures and high catalyst cost.
Other catalysts that have been employed such as those described in U.S. Pat. Nos. 1,774,089; 1,882,564; 2,327,053; 2,527,970; 2,807,651; and 3,354,227 which describe, among others, as catalysts sulfates of polyand divalent metals; dialkyl sulfates; zinc, nickel and chromium sulfates; metal, alkali metal and alkaline earth metal salts; metal chlorides and sulfur dioxide. These catalysts suffer from several disadvantages including formation of undesirable amounts of impurity products such as dioxane, aldehydes and polymers and too high solubilities which make these catalysts difficult to remove from the reaction mixture. Further disadvantages of some of these catalysts include slow reaction rates and excessive toxicity and corrosivity.
Heretofore, a catalyst that is substantially insoluble in the reaction mixture (heterogeneous) has not been described which also allows the particular process advantages hereinafter described.